Pulmonary valve should open shortly after the onset of RV systole , when RV pressure exceeds the PA end diastolic pressure which will be around 10-15 mmHg.
We know cardiac valves open and close with reference to the pressure difference across the valve .So, in any part of cardiac cycle , if RV pressure exceeds the pulmonary arterial pressure , pulmonary valve is bound to open. (The pulmonary leaflets simply doesn’t bother whether RV is in systole or diastole )
What are the situations RV pressure may exceed PA pressure during diastole ?
Yes, if RVEDP raises for any reasons beyond 15 mmhg it can prematurely open the pulmonary valve in late diastole. This often coincides with right atrial contraction that make the RVEDP to spike just before systole. In chronic right heart dysfunction the premature opening can occur much earlier in diastole and not dependent on RA contraction. It can even be noted with AF if the mean RVEDP exceeds PA pressures.
This typically happen in constrictive pericardits and any isolated RV failure without pulmonary hypertension.(Please note , for premature pulmonary valve opening to occur one important prerequisite is, PA pressure should be normal or low and hence its precluded in significant pulmonary hypertension )
Conditions associated with premature PV opening
1. Constrictive pericarditis.
2. Isolated RV restrictive cardiomyopathy (Lofflers etc .Note :Biventricular restriction would prevent premature opening as PA pressure is raised. )
3. Ebstein anomaly
4.Some patients with with RSOV .(Acute raise in RVEDP)
5.Post tricsupid valvotomy